Method and apparatus for handling ran assistance information for radio link failure in wireless communication system

ABSTRACT

A method and apparatus for handling radio access network (RAN) assistance information in a wireless communication system is provided. A user equipment (UE) discards first broadcast RAN assistance information when a radio link failure (RLF) occurs, and applies second broadcast RAN assistance information after a specific time. That is, upon RLF, until when received broadcast RAN assistance information is not applied is defined.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to wireless communications, and moreparticularly, to a method and apparatus for handling radio accessnetwork (RAN) assistance information for radio link failure (RLF) in awireless communication system.

Related Art

3rd generation partnership project (3GPP) long-term evolution (LTE) is atechnology for enabling high-speed packet communications. Many schemeshave been proposed for the LTE objective including those that aim toreduce user and provider costs, improve service quality, and expand andimprove coverage and system capacity. The 3GPP LTE requires reduced costper bit, increased service availability, flexible use of a frequencyband, a simple structure, an open interface, and adequate powerconsumption of a terminal as an upper-level requirement.

3GPP/wireless local area network (WLAN) interworking has been discussed.3GPP/WLAN interworking may be called traffic steering. From rel-8 of3GPP LTE, access network discovery and selection functions (ANDSF) fordetecting and selecting accessible access networks have beenstandardized while interworking with non-3GPP access (e.g., WLAN) isintroduced. The ANDSF may carry detection information of access networksaccessible in location of a user equipment (UE) (e.g., WLAN, WiMAXlocation information, etc), inter-system mobility policies (ISMP) whichis able to reflect operator's policies, and inter-system routing policy(ISRP). Based on the information described above, the UE may determinewhich Internet protocol (IP) traffic is transmitted through which accessnetwork. The ISMP may include network selection rules for the UE toselect one active access network connection (e.g., WLAN or 3GPP). TheISRP may include network selection rules for the UE to select one ormore potential active access network connection (e.g., both WLAN and3GPP). The ISRP may include multiple access connectivity (MAPCON), IPflow mobility (IFOM) and non-seamless WLAN offloading. Open mobilealliance (OMA) device management (DM) may be used for dynamic provisionbetween the ANDSF and the UE.

The MAPCON is a standardization of a technology which enablesconfiguring and maintaining multiple packet data network (PDN)connectivity simultaneously through 3GPP access and non-3GPP access, andenables a seamless traffic offloading in units of all active PDNconnections. For this, an ANDSF server provides access point name (APN)information for performing offloading, routing rule, time of dayinformation, and validity area information, etc.

The IFOM supports mobility in a unit of IP flow, which is more flexibleand more segmented than the MAPCON, and seamless offloading. The IFOMenables access to different access networks even when the UE isconnected to a PDN using the same APN, which is different from theMAPCON. The IFOM also enables mobility in a unit of specific IP trafficflow, not a unit of PDN, for a unit of mobility or offloading, andaccordingly, services may be provided flexibly. For this, an ANDSFserver provides IP flow information for performing offloading, routingrule, time of day information, and validity area information, etc.

The non-seamless WLAN offloading is a technology that offloads trafficscompletely so as not to go through the evolved packet core (EPC) as wellas that changes a path of a specific IP traffic to WLAN. The offloadedIP traffic cannot be moved to 3GPP access seamlessly again sinceanchoring is not performed to the P-GW for mobility support. For this,an ANDSF server provides information as similar as the informationprovided for the IFOM.

For efficient traffic steering between 3GPP/WLAN, radio access network(RAN) assistance information may be provided by the network. Duringradio link failure (RLF), how to handle the RAN assistance informationmay need to be defined.

SUMMARY OF THE INVENTION

The present invention provides a method and apparatus for handling radioaccess network (RAN) assistance information for radio link failure (RLF)in a wireless communication system. The present invention provides amethod and apparatus for defining until when broadcast RAN assistanceinformation is not applied upon RLF.

In an aspect, a method for handling, by a user equipment (UE), radioaccess network (RAN) assistance information in a wireless communicationsystem is provided. The method includes discarding first broadcast RANassistance information when a radio link failure (RLF) occurs, andapplying second broadcast RAN assistance information after a specifictime.

In another aspect, a user equipment (UE) includes a memory, atransceiver, and a processor coupled to the memory and the transceiver,and configured to discard first broadcast radio access network (RAN)assistance information when a radio link failure (RLF) occurs, and applysecond broadcast RAN assistance information after a specific time.

Upon RLF, until when broadcast RAN assistance information is not appliedcan be clear.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem.

FIG. 4 shows a block diagram of a control plane protocol stack of an LTEsystem.

FIG. 5 shows an example of a physical channel structure.

FIG. 6 shows a graphical representation of Wi-Fi channels in 2.4 GHzband.

FIG. 7 shows an example of a method for handling RAN assistanceinformation according to an embodiment of the present invention.

FIG. 8 shows a wireless communication system to implement an embodimentof the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wirelesscommunication systems such as code division multiple access (CDMA),frequency division multiple access (FDMA), time division multiple access(TDMA), orthogonal frequency division multiple access (OFDMA), singlecarrier frequency division multiple access (SC-FDMA), etc. The CDMA canbe implemented with a radio technology such as universal terrestrialradio access (UTRA) or CDMA-2000. The TDMA can be implemented with aradio technology such as global system for mobile communications(GSM)/general packet ratio service (GPRS)/enhanced data rate for GSMevolution (EDGE). The OFDMA can be implemented with a radio technologysuch as institute of electrical and electronics engineers (IEEE) 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), etc.IEEE 802.16m is an evolution of IEEE 802.16e, and provides backwardcompatibility with an IEEE 802.16-based system. The UTRA is a part of auniversal mobile telecommunication system (UMTS). 3rd generationpartnership project (3GPP) long term evolution (LTE) is a part of anevolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA indownlink and uses the SC-FDMA in uplink. LTE-advance (LTE-A) is anevolution of the 3GPP LTE.

For clarity, the following description will focus on the LTE-A. However,technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network iswidely deployed to provide a variety of communication services such asvoice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or moreuser equipment (UE; 10), an evolved-UMTS terrestrial radio accessnetwork (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers toa communication equipment carried by a user. The UE 10 may be fixed ormobile, and may be referred to as another terminology, such as a mobilestation (MS), a user terminal (UT), a subscriber station (SS), awireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and aplurality of UEs may be located in one cell. The eNB 20 provides an endpoint of a control plane and a user plane to the UE 10. The eNB 20 isgenerally a fixed station that communicates with the UE 10 and may bereferred to as another terminology, such as a base station (BS), anaccess point, etc. One eNB 20 may be deployed per cell.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 tothe UE 10, and an uplink (UL) denotes communication from the UE 10 tothe eNB 20. In the DL, a transmitter may be a part of the eNB 20, and areceiver may be a part of the UE 10. In the UL, the transmitter may be apart of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) and a systemarchitecture evolution (SAE) gateway (S-GW). The MME/S-GW 30 may bepositioned at the end of the network and connected to an externalnetwork. For clarity, MME/S-GW 30 will be referred to herein simply as a“gateway,” but it is understood that this entity includes both the MMEand S-GW.

The MME provides various functions including non-access stratum (NAS)signaling to eNBs 20, NAS signaling security, access stratum (AS)security control, inter core network (CN) node signaling for mobilitybetween 3GPP access networks, idle mode UE reachability (includingcontrol and execution of paging retransmission), tracking area listmanagement (for UE in idle and active mode), packet data network (PDN)gateway (P-GW) and S-GW selection, MME selection for handovers with MMEchange, serving GPRS support node (SGSN) selection for handovers to 2Gor 3G 3GPP access networks, roaming, authentication, bearer managementfunctions including dedicated bearer establishment, support for publicwarning system (PWS) (which includes earthquake and tsunami warningsystem (ETWS) and commercial mobile alert system (CMAS)) messagetransmission. The S-GW host provides assorted functions includingper-user based packet filtering (by e.g., deep packet inspection),lawful interception, UE Internet protocol (IP) address allocation,transport level packet marking in the DL, UL and DL service levelcharging, gating and rate enforcement, DL rate enforcement based onaccess point name aggregate maximum bit rate (APN-AMBR).

Interfaces for transmitting user traffic or control traffic may be used.The UE 10 is connected to the eNB 20 via a Uu interface. The eNBs 20 areconnected to each other via an X2 interface. Neighboring eNBs may have ameshed network structure that has the X2 interface. A plurality of nodesmay be connected between the eNB 20 and the gateway 30 via an S1interface.

FIG. 2 shows a block diagram of architecture of a typical E-UTRAN and atypical EPC. Referring to FIG. 2, the eNB 20 may perform functions ofselection for gateway 30, routing toward the gateway 30 during a radioresource control (RRC) activation, scheduling and transmitting of pagingmessages, scheduling and transmitting of broadcast channel (BCH)information, dynamic allocation of resources to the UEs 10 in both ULand DL, configuration and provisioning of eNB measurements, radio bearercontrol, radio admission control (RAC), and connection mobility controlin LTE ACTIVE state. In the EPC, and as noted above, gateway 30 mayperform functions of paging origination, LTE IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 shows a block diagram of a user plane protocol stack of an LTEsystem. FIG. 4 shows a block diagram of a control plane protocol stackof an LTE system. Layers of a radio interface protocol between the UEand the E-UTRAN may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on the lower three layers ofthe open system interconnection (OSI) model that is well-known in thecommunication system.

A physical (PHY) layer belongs to the L1. The PHY layer provides ahigher layer with an information transfer service through a physicalchannel. The PHY layer is connected to a medium access control (MAC)layer, which is a higher layer of the PHY layer, through a transportchannel. A physical channel is mapped to the transport channel. Databetween the MAC layer and the PHY layer is transferred through thetransport channel. Between different PHY layers, i.e., between a PHYlayer of a transmission side and a PHY layer of a reception side, datais transferred via the physical channel.

A MAC layer, a radio link control (RLC) layer, and a packet dataconvergence protocol (PDCP) layer belong to the L2. The MAC layerprovides services to the RLC layer, which is a higher layer of the MAClayer, via a logical channel. The MAC layer provides data transferservices on logical channels. The RLC layer supports the transmission ofdata with reliability. Meanwhile, a function of the RLC layer may beimplemented with a functional block inside the MAC layer. In this case,the RLC layer may not exist. The PDCP layer provides a function ofheader compression function that reduces unnecessary control informationsuch that data being transmitted by employing IP packets, such as IPv4or Ipv6, can be efficiently transmitted over a radio interface that hasa relatively small bandwidth.

A radio resource control (RRC) layer belongs to the L3. The RLC layer islocated at the lowest portion of the L3, and is only defined in thecontrol plane. The RRC layer controls logical channels, transportchannels, and physical channels in relation to the configuration,reconfiguration, and release of radio bearers (RBs). The RB signifies aservice provided the L2 for data transmission between the UE andE-UTRAN.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB onthe network side) may perform functions such as scheduling, automaticrepeat request (ARQ), and hybrid ARQ (HARQ). The PDCP layer (terminatedin the eNB on the network side) may perform the user plane functionssuch as header compression, integrity protection, and ciphering.

Referring to FIG. 4, the RLC and MAC layers (terminated in the eNB onthe network side) may perform the same functions for the control plane.The RRC layer (terminated in the eNB on the network side) may performfunctions such as broadcasting, paging, RRC connection management, RBcontrol, mobility functions, and UE measurement reporting andcontrolling. The NAS control protocol (terminated in the MME of gatewayon the network side) may perform functions such as a SAE bearermanagement, authentication, LTE_IDLE mobility handling, pagingorigination in LTE_IDLE, and security control for the signaling betweenthe gateway and UE.

FIG. 5 shows an example of a physical channel structure. A physicalchannel transfers signaling and data between PHY layer of the UE and eNBwith a radio resource. A physical channel consists of a plurality ofsubframes in time domain and a plurality of subcarriers in frequencydomain. One subframe, which is 1 ms, consists of a plurality of symbolsin the time domain. Specific symbol(s) of the subframe, such as thefirst symbol of the subframe, may be used for a physical downlinkcontrol channel (PDCCH). The PDCCH carries dynamic allocated resources,such as a physical resource block (PRB) and modulation and coding scheme(MCS).

A DL transport channel includes a broadcast channel (BCH) used fortransmitting system information, a paging channel (PCH) used for paginga UE, a downlink shared channel (DL-SCH) used for transmitting usertraffic or control signals, a multicast channel (MCH) used for multicastor broadcast service transmission. The DL-SCH supports HARQ, dynamiclink adaptation by varying the modulation, coding and transmit power,and both dynamic and semi-static resource allocation. The DL-SCH alsomay enable broadcast in the entire cell and the use of beamforming.

A UL transport channel includes a random access channel (RACH) normallyused for initial access to a cell, a uplink shared channel (UL-SCH) fortransmitting user traffic or control signals, etc. The UL-SCH supportsHARQ and dynamic link adaptation by varying the transmit power andpotentially modulation and coding. The UL-SCH also may enable the use ofbeamforming.

The logical channels are classified into control channels fortransferring control plane information and traffic channels fortransferring user plane information, according to a type of transmittedinformation. That is, a set of logical channel types is defined fordifferent data transfer services offered by the MAC layer.

The control channels are used for transfer of control plane informationonly. The control channels provided by the MAC layer include a broadcastcontrol channel (BCCH), a paging control channel (PCCH), a commoncontrol channel (CCCH), a multicast control channel (MCCH) and adedicated control channel (DCCH). The BCCH is a downlink channel forbroadcasting system control information. The PCCH is a downlink channelthat transfers paging information and is used when the network does notknow the location cell of a UE. The CCCH is used by UEs having no RRCconnection with the network. The MCCH is a point-to-multipoint downlinkchannel used for transmitting multimedia broadcast multicast services(MBMS) control information from the network to a UE. The DCCH is apoint-to-point bi-directional channel used by UEs having an RRCconnection that transmits dedicated control information between a UE andthe network.

Traffic channels are used for the transfer of user plane informationonly. The traffic channels provided by the MAC layer include a dedicatedtraffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCHis a point-to-point channel, dedicated to one UE for the transfer ofuser information and can exist in both uplink and downlink. The MTCH isa point-to-multipoint downlink channel for transmitting traffic datafrom the network to the UE.

Uplink connections between logical channels and transport channelsinclude the DCCH that can be mapped to the UL-SCH, the DTCH that can bemapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH.Downlink connections between logical channels and transport channelsinclude the BCCH that can be mapped to the BCH or DL-SCH, the PCCH thatcan be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, andthe DTCH that can be mapped to the DL-SCH, the MCCH that can be mappedto the MCH, and the MTCH that can be mapped to the MCH.

An RRC state indicates whether an RRC layer of the UE is logicallyconnected to an RRC layer of the E-UTRAN. The RRC state may be dividedinto two different states such as an RRC idle state (RRC_IDLE) and anRRC connected state (RRC_CONNECTED). In RRC_IDLE, the UE may receivebroadcasts of system information and paging information while the UEspecifies a discontinuous reception (DRX) configured by NAS, and the UEhas been allocated an identification (ID) which uniquely identifies theUE in a tracking area and may perform public land mobile network (PLMN)selection and cell re-selection. Also, in RRC_IDLE, no RRC context isstored in the eNB.

In RRC_CONNECTED, the UE has an E-UTRAN RRC connection and a context inthe E-UTRAN, such that transmitting and/or receiving data to/from theeNB becomes possible. Also, the UE can report channel qualityinformation and feedback information to the eNB. In RRC_CONNECTED, theE-UTRAN knows the cell to which the UE belongs. Therefore, the networkcan transmit and/or receive data to/from UE, the network can controlmobility (handover and inter-radio access technologies (RAT) cell changeorder to GSM EDGE radio access network (GERAN) with network assistedcell change (NACC)) of the UE, and the network can perform cellmeasurements for a neighboring cell.

In RRC_IDLE, the UE specifies the paging DRX cycle. Specifically, the UEmonitors a paging signal at a specific paging occasion of every UEspecific paging DRX cycle. The paging occasion is a time interval duringwhich a paging signal is transmitted. The UE has its own pagingoccasion. A paging message is transmitted over all cells belonging tothe same tracking area. If the UE moves from one tracking area (TA) toanother TA, the UE will send a tracking area update (TAU) message to thenetwork to update its location.

Wi-Fi is a popular technology that allows an electronic device toexchange data wirelessly (using radio waves) over a computer network,including high-speed Internet connections. The Wi-Fi Alliance definesWi-Fi as any “wireless local area network (WLAN) products that are basedon the IEEE 802.11 standards”. However, since most modern WLANs arebased on these standards, the term “Wi-Fi” is used in general English asa synonym for “WLAN”.

A device that can use Wi-Fi (such as a personal computer, video-gameconsole, smartphone, tablet, or digital audio player) can connect to anetwork resource such as the Internet via a wireless network accesspoint. Such an access point (or hotspot) has a range of about 20 meters(65 feet) indoors and a greater range outdoors. Hotspot coverage cancomprise an area as small as a single room with walls that block radiowaves or as large as many square miles—this is achieved by usingmultiple overlapping access points.

The 802.11 family consist of a series of half-duplex over-the-airmodulation techniques that use the same basic protocol. The most popularare those defined by the 802.11b and 802.11g protocols, which areamendments to the original standard. 802.11-1997 was the first wirelessnetworking standard, but 802.11b was the first widely accepted one,followed by 802.11g and 802.11n. 802.11n is a new multi-streamingmodulation technique. Other standards in the family (c-f, h, j) areservice amendments and extensions or corrections to the previousspecifications.

802.11b and 802.11g use the 2.4 GHz industry-science-medical (ISM) band,operating in the United States under Part 15 of the US FederalCommunications Commission (FCC) Rules and Regulations. Because of thischoice of frequency band, 802.11b and g equipment may occasionallysuffer interference from microwave ovens, cordless telephones andBluetooth devices. 802.11b and 802.11g control their interference andsusceptibility to interference by using direct-sequence spread spectrum(DSSS) and OFDM signaling methods, respectively. 802.11a uses the 5 GHzU-NII band, which, for much of the world, offers at least 23non-overlapping channels rather than the 2.4 GHz ISM frequency band,where adjacent channels overlap. Better or worse performance with higheror lower frequencies (channels) may be realized, depending on theenvironment.

The segment of the radio frequency spectrum used by 802.11 variesbetween countries. In the US, 802.11a and 802.11g devices may beoperated without a license, as allowed in Part 15 of the FCC Rules andRegulations. Frequencies used by channels one through six of 802.11b and802.11g fall within the 2.4 GHz amateur radio band. Licensed amateurradio operators may operate 802.11b/g devices under Part 97 of the FCCRules and Regulations, allowing increased power output but notcommercial content or encryption.

FIG. 6 shows a graphical representation of Wi-Fi channels in 2.4 GHzband. 802.11 divides each of the above-described bands into channels,analogous to the way radio and TV broadcast bands are sub-divided. Forexample the 2.4000-2.4835 GHz band is divided into 13 channels spaced 5MHz apart, with channel 1 centered on 2.412 GHz and 13 on 2.472 GHz (towhich Japan added a 14^(th) channel 12 MHz above channel 13 which wasonly allowed for 802.11b). 802.11b was based on DSSS with a totalchannel width of 22 MHz and did not have steep skirts. Consequently onlythree channels do not overlap. Even now, many devices are shipped withchannels 1, 6 and 11 as preset options even though with the newer802.11g standard there are four non-overlapping channels—1, 5, 9 and 13.There are now four because the OFDM modulated 802.11g channels are 20MHz wide.

In addition to specifying the channel center frequency, 802.11 alsospecifies a spectral mask defining the permitted power distributionacross each channel. The mask requires the signal be attenuated aminimum of 20 dB from its peak amplitude at ±11 MHz from the centerfrequency, the point at which a channel is effectively 22 MHz wide. Oneconsequence is that stations can only use every fourth or fifth channelwithout overlap, typically 1, 6 and 11 in the Americas, and in theory,1, 5, 9 and 13 in Europe although 1, 6, and 11 is typical there too.Another is that channels 1-13 effectively require the band 2.401-2.483GHz, the actual allocations being, for example, 2.400-2.4835 GHz in theUK, 2.402-2.4735 GHz in the US, etc.

Since rel-8, 3GPP has standardized access network discovery andselection functions (ANDSF), which is for interworking between 3GPPaccess network and non-3GPP access network (e.g. WLAN). The ANDSF iselaborated in 3GPP TS 24.312. The ANDSF management object (MO) is usedto manage inter-system mobility policy (ISMP) and inter-system routingpolicy (ISRP) as well as access network discovery information stored ina UE supporting provisioning of such information from an ANDSF. TheANDSF may initiate the provision of information from the ANDSF to theUE. The UE may initiate the provision of all available information fromthe ANDSF, using a client-initiated session alert message. The relationbetween ISMP, ISRP and discovery information is that ISMP prioritize theaccess network when the UE is not capable to connect to the EPC throughmultiple accesses, ISRP indicate how to distribute traffic amongavailable accesses when the UE is capable to connect to the EPC throughmultiple accesses (i.e. the UE is configured for IP flow mobility(IFOM), multiple access connectivity (MAPCON), non-seamless WLAN offloador any combination of these capabilities), while discovery informationprovide further information for the UE to access the access networkdefined in the ISMP or in the ISRP. The MO defines validity areas,position of the UE and availability of access networks in terms ofgeographical coordinates. The UE is not required to switch on all UE'ssupported radios for deducing its location for ANDSF purposes or forevaluating the validity area condition of a policy or discoveryinformation. The UE shall discard any node which is a child of the ANDSFMO root node and is not supported by the UE. The ANDSF server shalldiscard any node which is a child of the ANDSF MO root node and is notsupported by the ANDSF server.

The UE may be provisioned with multiple valid ISMP, ISRP, inter-APNrouting policies (IARP) and WLAN selection policies (WLANSP) rules (bythe home PLMN (HPLMN) and by the visited PLMN (VPLMN) when it isroaming). The UE does not apply all these valid rules but selects andapplies only the “active” rules. Specifically:

-   -   A UE that cannot simultaneously route IP traffic over 3GPP        access and over WLAN access shall select an active ISMP rule, an        active IARP rule and an active WLANSP rule, as specified below.    -   A UE that can simultaneously route IP traffic over 3GPP access        and over WLAN access shall select an active ISRP rule, an active        IARP rule and an active WLANSP rule, as specified below.

When the UE is not roaming, it shall select the active ISMP/ISRP rule,the active IARP rule and the active WLANSP rule to apply from the validrules provided by the HPLMN based on the individual priorities of theserules (or based on other criteria). For example, the highest priorityvalid WLANSP rule is selected as the active WLANSP rule.

When the UE is roaming, it may have valid rules from both HPLMN andVPLMN. In this case, the UE shall select the active rules as follows:

1) The active IARP rule is selected from the valid IARP rules providedby the HPLMN.

2) The active ISMP/ISRP rule and the active WLANSP rule are selectedbased on the UE configuration as follows:

a) The UE is configured to “prefer WLAN selection rules provided by theHPLMN” or not. This configuration can be done either by the user or bythe home ANDSF (H-ANDSF) via the list of “VPLMNs with preferred WLANSelection Rules”. User configuration takes precedence over the H-ANDSFconfiguration.

b) If the UE is configured not to prefer WLAN selection rules providedby the HPLMN (i.e. the VPLMN to which the UE is registered is includedin the list of “VPLMNs with preferred WLAN Selection Rules”), then theUE shall check the WLANSP rule of the VPLMN and shall determine if thereare available WLAN access networks that match one or more groups ofselection criteria in this rule.

i) If there is at least one WLAN access network that matches one or moregroups of selection criteria in the WLANSP rule of the VPLMN, then theUE shall select the active WLANSP rule and the active ISMP/ISRP rulefrom the valid rules provided by the VPLMN (based on their priorityvalues).

ii) If there is no WLAN access network that matches one or more groupsof selection criteria in the WLANSP rule of the VPLMN, then the UE shallselect the active WLANSP rule and the active ISMP/ISRP rule from thevalid rules provided by the HPLMN. When the UE determines that at leastone WLAN access network that matches one or more groups of selectioncriteria in the WLANSP rule of the VPLMN becomes available, it shalloperate as in bullet i) above and may re-select to such WLAN accessnetwork.

c) If the UE is configured to prefer WLAN selection rules provided bythe HPLMN (i.e. the VPLMN to which the UE is registered is not includedin the list of “VPLMNs with preferred WLAN Selection Rules”), then theUE shall check the WLANSP rule of the HPLMN and shall determine if thereare available WLAN access networks that match one or more groups ofselection criteria in this rule.

i) If there is at least one WLAN access network that matches one or moregroups of selection criteria in the WLANSP rule of the HPLMN, then theUE shall select the active WLANSP rule and the active ISMP/ISRP rulefrom the valid rules provided by the HPLMN (based on their priorityvalues).

ii) If there is no WLAN access network that matches one or more groupsof selection criteria in the WLANSP rule of the HPLMN, then the UE shallselect the active WLANSP rule and the active ISMP/ISRP rule from thevalid rules provided by the VPLMN. When the UE determines that at leastone WLAN access network that matches one or more groups of selectioncriteria in the WLANSP rule of the HPLMN becomes available, it shalloperate as in bullet i) above and may re-select to such WLAN accessnetwork.

During power-up, while the UE has not registered to any PLMN, the UEshall consider the WLANSP rules provided by the HPLMN as valid and shallselect an active WLANSP rule as described above (the one with thehighest priority). Thus during power-up the UE can select a WLAN networkbased on the WLANSP rules provided by HPLMN.

In addition to ANDSF, additional policy may be specified in RANspecification for interworking between 3GPP access network and non-3GPPaccess network (e.g. WLAN). The additional policy for interworkingbetween 3GPP access network and non-3GPP access network may be referredto as RAN rules. The RAN rule may indicate condition(s) in which the UEis allowed/required to perform traffic steering from 3GPP LTE to WLAN orvice versa. The condition may involve evaluation of measurement resultsof 3GPP LTE cell, where the measurement result is compared with arelevant RAN rule parameter (i.e., measurement threshold) included inthe RAN assistance information. The condition may also involveevaluation of measurement results of WLAN, where the measurement resultis compared with a relevant RAN rule parameter (i.e., measurementthreshold) indicated by the RAN assistance information.

For ANDSF and RAN rule, the following RAN assistance parameters (orinformation) may be provided by the RAN and used by the RAN rules andthe ANDSF. The RAN assistance information may be provided to the UE viabroadcast signaling, i.e. in SystemInformationBlockType17, or viadedicated signaling, i.e. in the RRCConnectionReconfiguration message.The RAN assistance information received in SystemInformationBlockType17is valid only if the UE is camped on a suitable cell. The following RANassistance parameters provided by the RAN may replace correspondingparameters in ANDSF and RAN rule.

-   -   LTE reference signal received power (RSRP)/UMTS common pilot        channel (CPICH) received signal code power (RSCP) threshold (for        frequency division duplex (FDD))/UMTS primary common control        physical channel (PCCPCH) RSCP threshold (for time division        duplex (TDD))    -   LTE reference signal received quality (RSRQ)/UMTS CPICH Ec/No        threshold (for FDD)    -   WLAN channel utilization in the basic service set (BSS) load IE        (MaximumBSSLoadValue) threshold (the parameter is used 1-way for        determining offload possibility from 3GPP to WLAN or        alternatively hysteresis is used to prevent ping-pong)    -   Available WLAN DL and UL backhaul data rate        (MinBackhaulThreshold) threshold (the parameter is used 1-way        for determining offload possibility from 3GPP to WLAN or        hysteresis is used to prevent ping-pong)

*Further, offload preference indicator (OPI) may be provided by the RANand used by the ANDSF. The OPI value provided by the RAN is compared toa comparison-value provided in the ANDSF policy using an “equalto”—comparison (e.g. OPI_pointer=OPI value) or a “greater/lessthan”—comparison (e.g. OPI_threshold≧OPI_value) or may be compared to abitmap (e.g. a set of allowed OPI values) to trigger specific actions,e.g.:

1. OPI may be used in ANDSF to differentiate subscriber subgroups, i.e.gold/silver/bronze. For instance, different subscriber subgroups mayhave different OPI thresholds/pointers in their ANDSF policies, so thatbronze users are offloaded to WLAN first (when cellular load slightlyincreases) and gold users are kept on LTE till LTE capacity allows so.

2. OPI may be used to differentiate between traffic types, e.g. ANDSFISRP policies for different IP flows may have different OPIthresholds/pointers so that best effort traffic is offloaded to WLANfirst (when cellular load slightly increases).

3. OPI may also be used to trigger specific parts of ANDSF policiesand/or ANDSF MOs, OPI may be signaled to the UE in the form of a bitmapwhich may be compared to a bitmap (e.g. a set of allowed OPI values)stored in the ANDSF to trigger specific parts of ANDSF policies and/orANDSF MOs. In this case, OPI value may be considered as kind of ANDSF MOindex if there are multiple ANDSF MOs.

Examples and clarifications regarding RAN assistance parameters usage inRAN rules and ANDSF are described below. For each parameter “xxx”, theremay be two thresholds indicated by the RAN, i.e. “thresXxxLow” for lowerthreshold, and “thresXxxHigh” for higher threshold.

For 3GPP LTE, the RAN assistance parameters may be used for trafficsteering between 3GPP/WLAN as follows. The UE shall move traffic (e.g.for offloadable access point name (APN)) from 3GPP to WLAN if all thefollowing conditions are fulfilled if corresponding parameters arebroadcast or send with dedicated signaling:

-   -   Rsrp<threshRsrpLow or Rsrq<threshRsrqLow    -   bssLoad<threshBssLoadLow    -   dlBackhaulRate>threshDlBackhaulRateHigh    -   ulBackhaulRate>threshUlBackhaulRateHigh

The UE shall move offloadable traffic from WLAN to 3GPP if one or moreof the following conditions is fulfilled if corresponding parameters arebroadcast or send with dedicated signaling:

-   -   Rsrp>threshRsrpHigh    -   Rsrq>threshRsrqHigh

For 3GPP UMTS, the RAN assistance parameters may be used for trafficsteering between 3GPP/WLAN as follows. The UE shall move traffic (e.g.for offloadable APN) from 3GPP to WLAN if all the following conditionsare fulfilled if corresponding parameters are broadcast or send withdedicated signaling:

-   -   Rscp<threshRscpLow or EcNo<threshEcNoLow    -   bssLoad<threshBssLoadLow    -   dlBackhaulRate>threshDlBackhaulRateHigh    -   ulBackhaulRate>threshUlBackhaulRateHigh

The UE shall move offloadable traffic from WLAN to 3GPP if one or moreof the following conditions is fulfilled if corresponding parameters arebroadcast or send with dedicated signaling:

-   -   Rscp>threshRscpHigh    -   EcNo>threshEcNoHigh

Currently, a UE in RRC_CONNECTED in 3GPP LTE or CELL DCH (or CELL_FACH)in UMTS may apply RAN assistance information received via dedicatedsignaling (hereinafter, dedicated RAN assistance information) if suchhas been received. Otherwise, the UE may apply RAN assistanceinformation received via broadcast signaling (hereinafter, broadcast RANassistance information). Further, the UE may keep and apply thededicated RAN assistance information when the UE is in RRC_IDLE in LTE,or CELL_PCH (or URA_PCH) in UMTS, until a time T has passed since the UEhas entered RRC_IDLE in 3GPP LTE, or CELL_PCH (or URA_PCH) in UMTS,thereafter the UE may apply the broadcast RAN assistance information.That is, the dedicated RAN assistance information is applied while atimer is running, and upon expiry of the timer, the dedicated RANassistance information is discarded and the broadcast RAN assistanceinformation is applied. However, currently it is not clear how to handlethe broadcast RAN assistance information upon radio link failure (RLF).

In order to solve the problem described above, a method for handling RANassistance information for RLF according to an embodiment of the presentinvention is described below.

FIG. 7 shows an example of a method for handling RAN assistanceinformation according to an embodiment of the present invention.

In step S100, the UE discards dedicated RAN assistance information andfirst broadcast RAN assistance information when RLF occurs.Alternatively, the UE discards dedicated RAN assistance information whenthe UE selects or reselects a cell, which is not the primary cell(PCell) where the dedicated RAN assistance information was configured,after RLF occurs. The UE may stop using the dedicated/first broadcastRAN assistance information or remove the dedicated/first RAN broadcastassistance information.

In step S110, the UE applies second broadcast RAN assistance informationafter a specific time. For example, the UE may receive the secondbroadcast RAN assistance information via system information during a RRCconnection re-establishment procedure after the RLF occurs. However,upon acquisition of the second broadcast RAN assistance information viasystem information during the RRC connection re-establishment procedure,the UE may not apply the second broadcast RAN assistance information maynot perform RAN rule. The UE may apply the second broadcast RANassistance information after a successful completion of the RRCconnection re-establishment procedure (i.e. receivingRRCConnectionReestablishment message).

After the successful completion of the RRC connection re-establishmentprocedure, the UE may forward the second broadcast RAN assistanceinformation to upper layer for ANDSF.

Alternatively, the UE may receive the second broadcast RAN assistanceinformation via system information during a timer, i.e. T311 is runningafter the RLF occurs. However, upon acquisition of the second broadcastRAN assistance information during T311 is running, the UE may not applythe second broadcast RAN assistance information and may not perform RANrule. The UE may apply the second broadcast RAN assistance informationupon expiry or stop of T311. Upon expiry or stop of T311, the UE mayforward the second broadcast RAN assistance information to upper layerfor ANDSF.

Alternatively, from the time the UE declares the RLF until first RRCreconfiguration after successful RRC connection re-establishmentprocedure, the UE may not apply the second broadcast RAN assistanceinformation and may not perform RAN rule. After receiving the first RRCreconfiguration after the successful RRC connection re-establishmentprocedure, the UE may forward the second broadcast RAN assistanceinformation to upper layer for ANDSF.

FIG. 8 shows a wireless communication system to implement an embodimentof the present invention.

An eNB 800 may include a processor 810, a memory 820 and a transceiver830. The processor 810 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 810. The memory 820 is operatively coupled with the processor810 and stores a variety of information to operate the processor 810.The transceiver 830 is operatively coupled with the processor 810, andtransmits and/or receives a radio signal.

A UE 900 may include a processor 910, a memory 920 and a transceiver930. The processor 910 may be configured to implement proposedfunctions, procedures and/or methods described in this description.Layers of the radio interface protocol may be implemented in theprocessor 910. The memory 920 is operatively coupled with the processor910 and stores a variety of information to operate the processor 910.The transceiver 930 is operatively coupled with the processor 910, andtransmits and/or receives a radio signal.

The processors 810, 910 may include application-specific integratedcircuit (ASIC), other chipset, logic circuit and/or data processingdevice. The memories 820, 920 may include read-only memory (ROM), randomaccess memory (RAM), flash memory, memory card, storage medium and/orother storage device. The transceivers 830, 930 may include basebandcircuitry to process radio frequency signals. When the embodiments areimplemented in software, the techniques described herein can beimplemented with modules (e.g., procedures, functions, and so on) thatperform the functions described herein. The modules can be stored inmemories 820, 920 and executed by processors 810, 910. The memories 820,920 can be implemented within the processors 810, 910 or external to theprocessors 810, 910 in which case those can be communicatively coupledto the processors 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies thatmay be implemented in accordance with the disclosed subject matter havebeen described with reference to several flow diagrams. While forpurposed of simplicity, the methodologies are shown and described as aseries of steps or blocks, it is to be understood and appreciated thatthe claimed subject matter is not limited by the order of the steps orblocks, as some steps may occur in different orders or concurrently withother steps from what is depicted and described herein. Moreover, oneskilled in the art would understand that the steps illustrated in theflow diagram are not exclusive and other steps may be included or one ormore of the steps in the example flow diagram may be deleted withoutaffecting the scope and spirit of the present disclosure.

1. A method for handling, by a user equipment (UE), radio access network(RAN) assistance information in a wireless communication system, themethod comprising: discarding first broadcast RAN assistance informationwhen a radio link failure (RLF) occurs; and applying second broadcastRAN assistance information after a specific time.
 2. The method of claim1, further comprising receiving the second broadcast RAN assistanceinformation via system information during a radio resource control (RRC)connection re-establishment procedure after the RLF occurs.
 3. Themethod of claim 2, wherein the specific time corresponds to a successfulcompletion of the RRC connection re-establishment procedure.
 4. Themethod of claim 1, further comprising receiving the second broadcast RANassistance information via system information during a timer is runningafter the RLF occurs.
 5. The method of claim 4, wherein the specifictime corresponds to expiry or stop of the timer.
 6. The method of claim1, wherein the specific time corresponds to first RRC connectionreconfiguration after a successful RRC connection re-establishmentprocedure.
 7. The method of claim 1, wherein applying the secondbroadcast RAN assistance information comprises forwarding the secondbroadcast RAN assistance information to an upper layer for accessnetwork discovery and selection functions (ANDSF).
 8. The method ofclaim 1, further comprising discarding dedicated RAN assistanceinformation when the RLF occurs.
 9. The method of claim 1, furthercomprising discarding dedicated RAN assistance information when the acell, which is not a primary cell (PCell) where the dedicated RANassistance information was configured, is selected after the RLF occurs.10. A user equipment (UE) comprising: a memory; a transceiver; and aprocessor coupled to the memory and the transceiver, and configured to:discard first broadcast radio access network (RAN) assistanceinformation when a radio link failure (RLF) occurs; and apply secondbroadcast RAN assistance information after a specific time.
 11. The UEof claim 10, wherein the processor is further configured to control thetransceiver to receive the second broadcast RAN assistance informationvia system information during a radio resource control (RRC) connectionre-establishment procedure after the RLF occurs.
 12. The UE of claim 11,wherein the specific time corresponds to a successful completion of theRRC connection re-establishment procedure.
 13. The UE of claim 10,wherein the processor is further configured to control the transceiverto receive the second broadcast RAN assistance information via systeminformation during a timer is running after the RLF occurs.
 14. The UEof claim 13, wherein the specific time corresponds to expiry or stop ofthe timer.
 15. The UE of claim 10, wherein the specific time correspondsto first RRC connection reconfiguration after a successful RRCconnection re-establishment procedure.